The present invention relates generally to the field of optical filtering and, in particular, to an electro-optically tunable filter for the spectral filtering of light and/or optical radiation.
Filtering optical radiation has been important for many applications such as identifying chemicals or determining properties of materials. Early filtering was done by a prism. Light would pass through a prism and be disbursed into wavelengths or into a range of wavelengths, and then a certain light wavelength or range of wavelengths were allowed to pass through an aperture for detection. A spectral filter in this configuration was generally referred to as a spectrometer. As technology progressed, diffraction gratings were used to produce a select spectrum of light through the defraction grating as opposed to a prism. In either filtering case, the range of wavelengths being detected could be tuned by rotating the prism or, in the case of a defraction grating, rotating the detraction grating.
As the electronics industry progressed, the ability to control or tune apertures without the use of mechanical means became more desirable because it could be faster. Mechanical means involve moving parts and require more time to move parts (e.g., gratings). Furthermore, space is typically a consideration in certain applications where space is limited. Systems can be designed into smaller confines if mechanical movement is minimized.
In certain applications, it is desirous to use components that are more reliable, robust, and require minimal space. For example, in the space industry wherein satellites are launched into orbit for purposes of performing tests, components must endure stress and vibration, take less space, and provide accuracy.
Accordingly, there is a need for an optical filter that is tunable without moving parts. Such a filter would be space-efficient, robust and more accurate than mechanically tunable filters.
The present invention provides an electro-optically tunable filter for the spectral filtering of light and/or optical radiation.
One embodiment of the present invention includes an electro-optical crystal having diametrically opposed input and output portions. The crystal changes its refractive index when an electric field is applied to it. An electrically conductive mesh filter covers and is in electrical contact with the input portion of the crystal. An electrode covers and is in electrical contact with the output portion of the crystal. The electrically conductive mesh filter creates a narrow bandpass and carries electrical voltage to the crystal. The electrical voltage exits the crystal and passes through the electrode to a voltage source.
The mesh filter represents small-scaled window screens. When the mesh filter is placed on the crystal, the optical properties of the combination are determined partially by the refractive index of the crystal once a voltage is applied to the mesh screen. The refractive index of the crystal can be changed with the application of variable voltages, thereby creating varying spectral positions through the filter. Thin film coatings will be applied to the crystal.
Use of the filter will entail providing a light source that will travel through the mesh filter into the electro-optic crystal and will exit the crystal. Application of a voltage between the mesh filter and the electrode creates a field internal to the electro optic crystal that will change the refractive index of it and hence allow it to be tunable in the bandpass location.
A second embodiment of the present invention includes an electro-optical crystal having diametrically opposed input and output portions. The crystal changes its refractive index when an electric field is applied to it. A first electrically conductive mesh filter covers and is in electrical contact with the input portion of the crystal. An electrode covers and is in electrical contact with the output portion of the crystal. A second electrically conductive mesh filter covers, but does not contact, the electrode. The first electrically conductive mesh filter creates a narrow bandpass and carries electrical voltage to the crystal. The electrical voltage exits the crystal and passes through the electrode to a voltage source. The addition of the second electrically conductive mesh filter results in the emission of light pulses when a variable voltage is applied to a voltage source.
A third embodiment of the present invention includes an electro-optical crystal having diametrically opposed input and output portions. The crystal changes its refractive index when an electric field is applied to it. An electrically conductive mesh filter covers and is in electrical contact with input portion of the crystal. A first electrode is in electrical contact with the crystal on a side contiguous to the electrically conductive mesh filter. A second electrode is also in electrical contact with the crystal on a side both contiguous to the electrically conductive mesh filter and non-contiguous to the first electrode. The first electrode carries electrical voltage to the crystal. The electrical voltage exits the crystal and passes through the second electrode to a voltage source.